Plunger actuated coaxial switch



March 16, 1965 J. c. D! RUSSO ETAL 3,174,020

PLUNGER ACTUATED COAXIAL SWITCH Filed June 21, 1962 EN'roRs JOSEPH c. 0/ R 0 wmsw W/LLS TTORNEY r W A United States Patent 3,174,029 PLUNGER ACTUATED CQAXTAL SWETCH Joseph C. Di Russo, Freeport, and Andrew Wills, In,

Forest Hills, N.Y., assignors to Sperry Rand Corporati-on, Great Neck, N.Y., a corporation of Delaware Filed June 21, E52, Ser. No. 204,146 13 Claims. ((Il. 200-153) This invention relates to electrical switches and more particularly to improvements in high frequency coaxial switches.

Many prior art coaxial switches employ a section of coaxial line in which an intermediate portion of the center conductor can be moved out of contact with the input and output portions to open the switch. Although such switches are useful, a certain amount of leakage occurs between the input and output channels. This results in cross talk that can be troublesome in critical applications.

Furthermore, in many of these prior art switches, the movable elements operate within a metallic plunger cavity. The cavity is formed with such dimensions that it is liable to become resonant at certain frequencies within the range of interest. Since the movable elements do not seat in precisely the same position for each cycle of operation, the electrical characteristics of the switch change erratically from. one operating cycle to the next.

It is an object of the invention to provide a switch that is capable of operating over a wide band of frequencies.

It is another object of the invention to provide a coaxial switch with stable and predictable operating characteristics.

It is still another object of the invention to provide a coaxial switch that is relatively free from troublesome cross talk.

These and other objects are achieved in the present invention by providing a decoupling means that acts to minimize the transfer of leakage energy into the disconnected channels of the switch as well as to inhibit undesirable resonance effects.

The invention will be described with reference to the following drawings, wherein:

FIG. 1 is a View, partly in cross section, of a Y junction switch embodying the principles of the invention, and

FIG. 2 is an enlarged perspective view of a unitary decoupling means useful in practicing the invention.

FIG. 1 depicts a switch body 11 in which the periphery 13 contains an opening that forms the base of an elongated cavity 15. Coaxial fittings 17 and 19 support the extended center conductors 21 and 23 of input and output coaxial lines in operative relationship near the movable plunger 25. A neck portion 27 of the plunger supports an insulating body 29 in the cavity 15. A contacting member 31 is inserted in a transverse hole formed near the forward end of the plunger. The contacting member interconnects the extended center conductors 21 and 23 when the plunger is in the operative or extended position. The cavity 15 includes a counter bored base portion 33 and an inner cylindrical portion surrounding the insulating body 29. An annular dielectric bushing 35 surrounds the neck portion 27 of the plunger in the counterbored base portion of the cavity. The dielectric bushing preferably contains an annular recess in its outer flat surface as best shown in FIG. 1. Two conducting members in the form of spring fingers 37 are mounted on the dielectric bushing and extend along opposite sides of the plunger. FIG. 1 depicts the plunger 25 in a partially retracted position, however when the plunger is in the fully retracted position, the two fingers engage opposite ends of the contacting member 31. The

spring fingers are separately mounted on the dielectric bushing so as to be normally insulated from each other. These fingers, however, are pressed into contact with the switch body by means of the force applied by the plunger. A second plunger is actuated through the neck portion 39 in order to establish a circuit between the coaxial fittings 17 and 41.

When the plunger 25 is in the retracted position, the center conductors 21 and 23 are capacitively coupled to the contacting member 31. In prior art switches, this coupling provides a leakage path that permits energy to propagate between the mechanically disconnected center conductors. The leakage path must be made sufficiently long to reduce the cross talk to an acceptable level. This can be accomplished only by retracting the plunger a considerable distance.

By using the decoupling means of the present invention, leakage energy that is coupled to the contacting member from either coaxial line is diverted through the low impedance path to the switch body rather than being allowed to propagate to the opposite center conductor. This causes the cross talk to drop abruptly as soon as the spring fingers engage the contacting member. Since a long leakage path is now unnecessary, switches employing the principles of the invention require only a relatively short plunger stroke. This, in turn, increases the speed of switching and permits the use of simplified plunger driving means.

Previous attempts have been made to decouple such contacting members by attaching pairs of spring fingers to the walls of the plunger cavity so that the free ends of the fingers could engage opposite ends of the contacting member. Such decoupling means, however, are difficult to assemble or replace. Furthermore, such means do not overcome the problems of erratic behavior caused by cavity variations.

The spring fingers and the dielectric bushing of the present invention constitute a unitary decoupling means as best illustrated in FIG. 2. This decoupling means is simple to fabricate, is easily installed, and is readily replaceable. The dielectric bushing can be constructed so as to provide a snug fit in the oounterbored base portion of the radial cavity, and secured in place by any suitable means.

The dielectric bushing also functions as a plunger guide surrounding the neck portion of the movable plunger. Previous switches used metallic bushings for this purpose. The position of the plunger varies slightly from cycle to cycle of switch operation because of unavoidable mechanical inaccuracies. Therefore, the spacing between the various elements of the plunger and the bushing vary from cycle to cycle. In the case of switches having a metallic bushing or spring support member in this region, the variation causes erratic switch performances. The substitution of a dielectric bushing, however, overcomes this problem since the presence of a non-conducting material has no practical influence on the switch characteristics.

In a typical installation, a Y-junction switch was modified by using a dielectric bushing that was made from a disc of nylon approximately in diameter. The spring fingers were spaced approximately 7 from each other, and were fabricated from strips of plated beryllium copper approximately wide.

The isolation between channels of the switch was measured and found to be in excess of 30 db in a frequency range extending up to 12 kmc.

Although bushings can be made conveniently from nylon, other suitable dielectric materials can be used for this purpose.

Furthermore, although the spring fingers 37 are cong a veniently formed with a straight shank and a hook-shaped contacting portion as shown in FIG. 2, variations of this shape are permissible. This particular shape was selected because it is simple to fabricate and has a long life.

Spring fingers having a slightly arcuate shape also have been employed. These fingers are bowed so that they contact the cavity walls in an intermediate region and then curve inward so as to contact the plunger at the free ends of the fingers. The spring fingers are capable of adjusting to slight horizontal rotational movements of the insulating body.

Although the decoupling means has been described for use in a particular Y junction switch, it will be appreciated by those skilled in the art that the principles of the invention can be applied to a wide variety of switches in which a plunger moves a contact member between spaced transmission line elements to close the switch. Thus for example, T junction coaxial switches and straight-through coaxial switches often employ a plunger arrangement that could be modified according to the teachings of the present invention.

While the invention has been described in its prefer-red embodiments, it is to be understood that the words which have been used are words of description rather than of limitation and that changes Within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

What is claimed is:

1. An' electrical switch comprising a switch body, input and output coaxial lines supported in the switch body, a retractable plunger, a contacting member on the plunger for optionally interconnecting the coaxial lines, and a spring finger engaging the contacting member when the plunger is retracted, said spring finger being urged into contact with the switch body only by the force applied by said plunger.

2. An electrical switch comprising a switch body, input and output coaxial lines supported in the switch body, a retractable plunger, said plunger including a transverse contacting member for optionally interconnecting the coaxial lines, and a pair of spring fingers disposed along opposite sides of the plunger, said fingers engaging the ends of the contacting member when the plunger is retracted, said fingers also being urged into electrical con.- tact with the switch body only by lateral force applied by the plunger.

3. An electrical switch comprising a switch body, input and output coaxial lines supported in the switch body, a movable contacting member for optionally interconnecting said coaxial lines, a dielectric bushing, and first and second conducting members individually supported on the dielectric bushing, said conducting members being disposed in the path of the movable contacting member so as to engage opposite ends of the contacting member when the switch is open, said conducting members further contacting the switch body when engaging the contacting member.

4. An improved coaxial switch comprising a switch body containing an elongated cavity, a contacting member longitudinally movable in said cavity, a transverse dielectric bushing in said cavity, first and second spring fingers individually mounted on said bushing, said spring fingers engaging opposite ends of the contacting member when the switch is open.

5. A coaxial switch comprising:

(a) a switch body containing an elongated cavity,

(b) input and output coaxial fittings in said switch body,

(c) an extended center conductor from each of said coaxial fittings positioned near one end of said cavity,

(d) a contacting member to interconnect said center conductors when the switch is closed,

(e) said contacting member being retractable into the cavity when the switch is open, and

(f) a pair of spring fingers connecting each end of the contacting member to the switch body when the switch is open.

6. An improved coaxial switch comprising a switch body containing an elongated plunger cavity; a longitudinally movable plunger in'the cavity; said plunger including an insulating body, and a transverse contacting member on the forward end of the plunger; first and second longitudinahspring fingers slidably disposed on diametrically opposite sides of the plunger and engaging said contacting member when the plunger is retracted; and a transverse dielectric bushing inside the base portion of said cavity supporting said spring fingers.

7. In a coaxial switch of the type in which a switch body contains a cavity within which a movable plunger operates to interpose a contacting member between input and output coaxial lines, an improved replaceable decoupling means comprising a dielectric bushing dimensioned to fit snugly in a portion of said cavity, said bushing surrounding and supporting a portion of the movable plunger, a pair of spring fingers individually mounted on the bushing and connecting the opposite ends of said contacting member to the switch body when the plunger is retracted.

8. In a coaxial switch of the type in which a switch body contains a cavity within which a movable plunger operates to interpose a contacting member between input and output coaxial lines, an improved replaceable decoupling means comprising a dielectric bushing surrounding a portion of the movable plunger, and a pair of spring fingers individually mounted on said bushing, said fingers connecting the ends of said contacting member to the wall of the cavity'when the switch is open.

9. An improved Y junction coaxial switch comprising a switch body containing an elongated radial plunger cavity, said cavity including a cylindrical portion and a counterboard base portion near the periphery of the switch body, a longitudinally movable plunger mounted within the cavity, a transverse contacting member on the forward end of said plunger, a transverse dielectric bushing slidably supporting the plunger in the base portion of the cavity, first and second longitudinal spring fingers individually mounted on the dielectric bushing so as to contact the switch body in said cylindrical portion, said spring fingers being sufficiently long to engage opposite ends of the contacting member when the plunger is in a retracted position.

10. In a coaxial switch of the type in which a switch body contains a cavity within which a movable plunger operates to interpose a contacting member between input and output coaxial lines, an improved unitary decoupling means comprising a dielectric bushing surrounding a portion of the plunger, and'a pair of spring fingers individually mounted on the bushing and extending along opposite sides of the plunger said fingers engaging the contacting member when the switch is open, said fingers further being pressed into contact with the switch body by the plunger.

11. In a coaxial switch of the type containing a switch body, input and output coaxial lines, and a movable contacting member to interconnect the coaxial lines as desired, an improved decoupling means comprising a dielectric bushing, and first and second conducting members individually mounted on said dielectric bushing so as to contact the switch body in a region intermediate the bushing and the contacting member, said first and second conducting members further engaging opposite ends of the contacting member only when the switch is open.

12. An electric switch comprising:

(a) a metallic switch body containing an elongated plunger cavity,

(b) a pair of coaxial transmission lines in the switch (c) an extended center conductor in each of said trans mission lines,

(d) a longitudinally movable plunger in said cavity,

(e) a contacting member on said plunger for interconnecting said center conductors when the plunger is in the extended position,

(f) first and second longitudinal spring fingers disposed on opposite sides of the plunger and, said fingers engaging said contacting member when the plunger is retracted, and

(g) a transverse dielectric bushing inside the plunger cavity supporting each spring finger individually so that the spring fingers are pressed into contact with the switch body.

13. An improved Y junction coaxial switch comprising:

(a) a metallic switch body containing an elongated radially disposed plunger cavity,

(b) a cylindrical portion in said cavity,

(c) a counterbored base portion in said cavity near the periphery of the switch body,

(d) a pair of coaxial transmission line fittings in said switch body,

(e) an extended center conductor in each coaxial fitting,

(f) a longitudinally movable plunger in said cavity,

(g) a contacting member on said plunger to intercon- 6 nect said extended conductors when the plunger is in the extended position, and (h) a unitary decoupling member including:

(a) an annular dielectric bushing dimensioned to provide a snug fit in said counterbored portion of the plunger cavity, and

(b) first and second longitudinal spring fingers mounted separately on said dielectric bushing so as to be insulated from each other but so as to contact the switch body in the region of the cylindrical cavity, said spring fingers being further disposed on opposite sides of the plunger, said fingers engaging said contacting member when the plunger is retracted.

References Cited by the Examiner UNITED STATES PATENTS 2,846,653 8/58 Lanctot et a1. 200153 20 BERNARD A. GILHEANY, Primary Examiner.

ROBERT K. SCHAEFER, Examiner. 

1. AN ELECTRICAL SWITCH COMPRISING A SWITCH BODY, INPUT AND OUTPUT COAXIAL LINES SUPPORTED IN THE SWITCH BODY, A RECTRACTABLE PLUNGER, A CONTACTING MEMBER ON THE PLUNGER FOR OPTIONALLY INTERCONNECTING THE COAXIAL LINES, AND A SPRING FINGER ENGAGING THE CONTACTING MEMBER WHEN THE PLUNGER IS RETRACTED, SAID SPRING FINGER BEING URGED INTO CONTACT WITH THE SWITCH BODY ONLY BY THE FORCE APPLIED BY SAID PLUNGER. 